Very low heat weight of my model after auto weight
If a bone doesn't have full control over part of your mesh, another bone is partially influencing it. Make sure the beginning and end of each bone are touching the mesh, so the automatic weighting works better.

In your screenshot it looks like bones from the left leg are influencing the right leg and vice versa. To get rid of this effect select the left leg in Edit Mode (e.g. go to wireframe, Box select the vertices from the left leg) and then remove the weight from any bone in the right leg or assign it a value of 0. Then repeat the other way around. (I recommend using "Remove")